Yes, the age limit is 16 to try and protect them from some of the physical and mental pressures before their bodies had had a chance of forming properly.
I did ballet and gymnastics (until my ballet teacher found out, freaked and banned me from doing gymnastics as well) and it does delay your body forming properly and the physical demands of keeping the right body shape and size. Eating disorders were rife due to the pressures of keeping the right size and shape.
I remember doing sessions of exercises of up to 50 sit ups, push ups etc... at 7/8 years old in ballet training and being screamed at for not pushing myself enough, once just for my bun daring to fall out of place by the school principal. I hate to imagine the physical and mental pressures on olympic standard children.